This application requests funds to support a central shared facility to study the electron spin resonance spectra of a variety of biological and chemical samples of an active group of researchers in the Department of Chemistry and National Magnet Laboratory at MIT. The facility will mainly serve a group of major users who currently hold active NIH research grants, but will also provide service to additional inorganic chemists and colleagues from other departments at MIT and to occasional outside users in the greater Boston/New England area. The instrument will be used by the principal groups to carry out research in the following areas: 1. Polyiron Centers in Chemistry and Biology. 2. Cytochrome P450 and Nitrogen Fixation Biochemistry. 3. Nickel Methanogenesis. 4. High Oxidation State Molybdenum and Tungsten Dinitrogen Complexes. 5. Technetium Radiopharmaceuticals and Related Technetium Chemistry. 6. ESR Studies of Organometallic Molecules and Multicomponent Redox Reagents. 7. Electronics and Magnetic Properties of Iron-Sulfur Protein Site Analogues.